System and method for controlling a report about link status monitoring result acquired by mobile station and transmitted to a base station

ABSTRACT

A radio measurement collection method in one embodiment is provided with: a step (S 142 ) wherein, in an idle state, radio-environment measurement is performed on a target LTE frequency band in accordance with measurement parameters set by an LTE base station (eNB); a step (S 143 ) wherein, in an idle state, radio-environment measurement is performed on a frequency band for a non-LTE radio access technology and/or an LTE frequency band other than the target frequency band; and a step (S 146 ) wherein, if the result of the measurement in step S 142  is less than a threshold, the result of the measurement in step S 142  and the result of the measurement in step S 143  are both logged together with location information.

TECHNICAL FIELD

The present invention relates to a radio measurement collection methodand a radio terminal with which it is possible to measure a radioenvironment and collect a measurement result.

BACKGROUND ART

In case of mobile communication systems, if a building is constructed onthe periphery of a radio base station and if the installation situationof the base stations on the periphery of the radio base station changes,then the radio environment related to this radio base station changes.Therefore, conventionally, an operator performs a drive test ofmeasuring a radio environment using a measurement vehicle provided witha measurement equipment, and collecting a measurement result andlocation information.

Such measurement and collection, for example, may contribute to theoptimization of the coverage of a radio base station, but face theproblem of too many man-hours and high cost. In this regard, accordingto 3GPP (3rd Generation Partnership Project) which is a project aimingto standardize a mobile communication system, a radio terminal owned bya user is used to proceed with the specification design of MDT(Minimization of Drive Test) for automation of the measurement andcollection (refer to Non Patent Literatures 1 and 2).

As a type of the MDT, there is a log-type MDT (hereinafter,appropriately Logged MDT). According to the Logged MDT, a radio terminalin an idle state (that is, a standby state) performs radio environmentmeasurement according to a preset measurement parameter, logs ameasurement result as MDT data together with location information andtime information, and holds the MDT data in order to report the MDT datato a network later. Using the MDT, the operator is able to recognize alocation (so-called a coverage hole) with low received power or receivedquality from a radio base station.

CITATION LIST Non Patent Literature

-   [NPL 1] 3GPP TR36.805 V9.0.0 “Study on Minimization of drive-tests    in Next Generation Networks”, 2009-12-   [NPL 2] 3GPP TS37.320 V0.7.0, “Radio measurement collection for    Minimization of Drive Tests (MDT)”, 2010-07

SUMMARY OF INVENTION

However, after an LTE (Long Term Evolution) technology withspecifications designed in 3GPP is introduced, it is considered to use aradio access technology (RAT) of both an LTE technology and a CDMAtechnology (W-CDMA or CDMA 2000), and it is expected to provide a radioterminal corresponding to a plurality of RATs. Furthermore, after theLTE technology is introduced, it is expected to provide a radio terminalcorresponding to a plurality of frequency bands.

There is a case in which even in a coverage hole at one frequency bandof one RAT, the radio terminal corresponding to the plurality of RATsand/or the plurality of frequency bands is able to be switched toanother RAT and/or another frequency band to perform communication.Accordingly, it is important for an operator to recognize whether thecoverage hole at one frequency band of one RAT is covered by the otherRAT and/or the other frequency band.

However, in the current MDT specifications, it is problematic that thereis no structure for recognizing whether the coverage hole at onefrequency band of one RAT is covered by the other RAT and/or the otherfrequency band.

Therefore, the present invention has been achieved in view of theabove-described problems, and an object thereof is to provide a radiomeasurement collection method and a radio terminal with which it ispossible to recognize whether a coverage hole at one frequency band ofone RAT is covered by another RAT and/or another frequency band.

In order solve the problems, the present invention has followingfeatures. First, a feature of a radio measurement collection method issummarized as a radio measurement collection method performed by a radioterminal (radio terminal UE), comprising: a step (step S11) of receivinga measurement configuration message for setting a measurement parameterincluding a frequency band to be measured, from a radio base station(e.g. LTE base station eNB) of a predetermined radio access technology;a first measurement step (step S142) of, in an idle state, performingradio environment measurement with respect to the frequency band to bemeasured of the predetermined radio access technology according to themeasurement parameter set by the measurement configuration message (e.g.MDT Configuration message); a second measurement step (step S143) of, inthe idle state, performing radio environment measurement with respect toa radio access technology different from the predetermined radio accesstechnology and/or a frequency band of the predetermined radio accesstechnology other than the frequency band to be measured; and a step(step S146) of logging both a measurement result in the firstmeasurement step and a measurement result in the second measurementstep, together with location information, when the measurement result inthe first measurement step is smaller than a threshold value.

According to such a feature, when the measurement result in the firstmeasurement step is smaller than a threshold value (that is, a coveragehole), the radio terminal logs both a measurement result in the firstmeasurement step and a measurement result in the second measurementstep, together with the location information. In this way, it ispossible to recognize whether a coverage hole at one frequency band ofone RAT is covered by another RAT and/or another frequency band.

Another feature of the radio measurement collection method according tothe present invention, in the radio measurement collection methodaccording to the aforementioned feature, is summarized as follows. Theradio measurement collection method comprises: a step (step S145) oflogging the measurement result in the first measurement step togetherwith the location information when the measurement result in the firstmeasurement step is equal to or more than the threshold value.

Another feature of the radio measurement collection method according tothe present invention, in the radio measurement collection methodaccording to the aforementioned feature, is summarized as follows. Inthe step of logging, frequency band information that indicates afrequency band at which the measurement in the second measurement stephas been performed, is further logged.

A feature of a radio measurement collection method is summarized as aradio measurement collection method performed by a radio terminal (radioterminal UE), comprising: a step (step S11) of receiving a measurementconfiguration message (e.g. MDT Configuration message) for setting ameasurement parameter including a frequency band to be measured, from aradio base station (e.g. LTE base station eNB) of a predetermined radioaccess technology; a step (step S143) of, in an idle state, performingradio environment measurement with respect to a radio access technologydifferent from the predetermined radio access technology and/or afrequency band of the predetermined radio access technology other thanthe frequency band to be measured; and a step (step S146) of logging ameasurement result in the step of performing the measurement, frequencyband information indicating a frequency band at which the measurement inthe step of performing the measurement has been performed, and locationinformation.

Another feature of the radio measurement collection method according tothe present invention, in the radio measurement collection methodaccording to the aforementioned feature, is summarized as follows. Theradio measurement collection method further comprises: a step (step S18)of transmitting the frequency band information logged in the step oflogging to a radio base station of the predetermined radio accesstechnology, together with the measurement result and the locationinformation, after the radio terminal is transitioned from an idle stateto a connected state.

A feature of a radio terminal is summarized as a radio terminalcomprising: a reception unit (radio communication unit 210) thatreceives a measurement configuration message (e.g. MDT Configurationmessage) for setting a measurement parameter including a frequency bandto be measured, from a radio base station (e.g. LTE base station eNB) ofa predetermined radio access technology; a first measurement unit (firstmeasurement unit 261) that, in an idle state, performs radio environmentmeasurement with respect to the frequency band to be measured of thepredetermined radio access technology according to the measurementparameter set by the measurement configuration message; a secondmeasurement unit (second measurement unit 262) that, in the idle state,performs radio environment measurement with respect to a radio accesstechnology different from the predetermined radio access technologyand/or a frequency band of the predetermined radio access technologyother than the frequency band to be measured; and a logging unit(logging unit 263) that logs both a measurement result in the firstmeasurement unit and a measurement result in the second measurementunit, together with location information, when the measurement result inthe first measurement unit is smaller than a threshold value.

Another feature of the radio terminal according to the presentinvention, in the radio terminal according to the aforementionedfeature, is summarized as follows. The logging unit further logsfrequency band information indicating a frequency band at which themeasurement has been performed by the second measurement unit.

A feature of a radio terminal is summarized as a radio terminalcomprising: a reception unit (radio communication unit 210) thatreceives a measurement configuration message (e.g. MDT Configurationmessage) for setting a measurement parameter including a frequency bandto be measured from a radio base station (e.g. LTE base station eNB) ofa predetermined radio access technology; a measurement unit (secondmeasurement unit 262) that, in an idle state, performs radio environmentmeasurement with respect to a radio access technology different from thepredetermined radio access technology and/or a frequency band of thepredetermined radio access technology other than the frequency band tobe measured; and a logging unit (logging unit 263) that logs ameasurement result of the measurement unit, frequency band informationindicating a frequency band at which the measurement has been performedby the measurement unit, and location information.

Another feature of the radio terminal according to the presentinvention, in the radio terminal according to the aforementionedfeature, is summarized as follows. The radio terminal further comprises:a transmission unit (report processing unit 264 and radio communicationunit 210) that transmits the frequency band information logged by thelogging unit to a radio base station of the predetermined radio accesstechnology, together with the measurement result and the locationinformation after the radio terminal is transitioned from an idle stateto a connected state.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating an entire schematic configuration of amobile communication system according to an embodiment of the presentinvention.

FIG. 2 is a diagram for explaining one example in which a communicationarea of an LTE base station of a frequency band F1, a communication areaof an LTE base station of a frequency band F2, and a communication areaof a radio base station of CDMA 2000 (a frequency band F3) overlap oneanother.

FIG. 3 is a block diagram illustrating a configuration of the LTE basestation according to the embodiment of the present invention.

FIG. 4 is a block diagram illustrating a configuration of a radioterminal according to the embodiment of the present invention.

FIG. 5 is an entire schematic sequence diagram illustrating a radiomeasurement collection method according to the embodiment of the presentinvention.

FIG. 6 is a flowchart illustrating details of a logging processaccording to the embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

With reference to the accompanying drawings, an embodiment of thepresent invention will be described in the sequence of (1) Overview ofmobile communication system, (2) Configuration of LTE base station, (3)Configuration of ratio terminal, (4) Radio measurement collectionmethod, (5) Effect of embodiment, and (6) Other embodiments. It is to benoted that the same or similar reference numerals are applied to thesame or similar parts through the drawings in the following embodiments.

A radio measurement collection method according to the presentembodiment is a radio measurement collection method performed by a radioterminal, and includes: a step of receiving an MDT Configuration message(corresponding to a measurement configuration message) for setting ameasurement parameter including a frequency band to be measured from anLTE base station (corresponding to a radio base station of apredetermined radio access technology); a first measurement step of, inan idle state, performing radio environment measurement with respect toan LTE frequency band to be measured according to the measurementparameter set by the MDT Configuration message; a second measurementstep of, in the idle state, performing radio environment measurementwith respect to a radio access technology different from LTE and/or anLTE frequency band other than the frequency band to be measured; and astep of logging both a measurement result in the first measurement stepand a measurement result in the second measurement step, together withlocation information when the measurement result in the firstmeasurement step is smaller than a threshold value.

Furthermore, in the present embodiment, in the step of logging,frequency band information that indicates a frequency band at which themeasurement in the second measurement step has been performed, isfurther logged.

(1) Overview of Mobile Communication System

FIG. 1 is a diagram illustrating an entire schematic configuration of amobile communication system 1 according to the present embodiment.

As illustrated in FIG. 1, the mobile communication system 1 includes aradio terminal UE (User Equipment), a plurality of radio base stationseNB (evolved Node-B), an operation and maintenance device OAM (Operationand Maintenance), and a mobility management device MME (MobilityManagement Entity)/a gateway device S-GW (Serving Gateway).

The plurality of radio base stations eNB constitute E-UTRAN(Evolved-UMTS Terrestrial Radio Access Network). Each of the pluralityof radio base stations eNB forms a cell that is a communication areawhere a service should be provided to the radio terminal UE. Note thatan LTE radio base station is called as an “LTE base station” in thefollowing, where appropriate.

Each of the adjacent radio base stations eNB can communicate mutuallyvia an X2 interface which is a logical communication channel to providecommunication between the base stations. Each of the plurality of radiobase stations eNB can communicate with EPC (Evolved Packet Core),specifically, the MME/S-GW via an S1 interface. Furthermore, each radiobase station eNB can communicate with the operation and maintenancedevice OAM managed by an operator.

Note that the E-UTRAN and the operation and maintenance device OAM aretogether called as “Network” in the following, where appropriate.However, a radio access network of different RAT may be included in the“Network”.

The radio terminal UE is a radio communication device owned by a user,and is also called as “User Equipment”. The radio terminal UE iscompatible with a plurality of RATs. In the present embodiment, theradio terminal UE is compatible with LTE and CDMA 2000.

Furthermore, the radio terminal UE is compatible with a plurality offrequency bands. In the present embodiment, the radio terminal UE iscompatible with a frequency band 1 of LTE, a frequency band 2 of LTE,and a frequency band 3 of CDMA 2000.

The mobile communication system 1 supports MDT (specifically, LoggedMDT). According to the Logged MDT, a radio terminal in an idle stateperforms radio environment measurement according to a preset measurementparameter, logs a measurement result as MDT data together with locationinformation and a time stamp, and holds the MDT data in order to reportthe MDT data to a network later. Using the MDT, the operator is able torecognize a location (so-called a coverage hole) with low received poweror received quality from a radio base station.

FIG. 2 is a diagram for explaining one example in which a communicationarea of an LTE base station of a frequency band F1, a communication areaof an LTE base station of a frequency band F2, and a communication areaof a radio base station of CDMA 2000 (a frequency band F3) overlap oneanother. Note that the radio base station of CDMA 2000 is called as a“CDMA 2000 base station” in the following, where appropriate.

As illustrated in FIG. 2, each of the communication area of the LTE basestation of the frequency band F1, the communication area of the LTE basestation of the frequency band F2, and the communication area of the CDMA2000 base station includes a coverage hole.

A coverage hole of the LTE (the frequency band F1) is covered by the LTE(the frequency band F2) and the CDMA 2000. When a radio terminal UEperforming communication using the LTE (the frequency band F1) movesinto the coverage hole of the LTE (the frequency band F1), the radioterminal UE is able to continuously perform communication by performinghandover to the LTE base station of the frequency band F2 or the CDMA2000 base station.

A coverage hole of the LTE (the frequency band F2) is covered by the LTE(the frequency band F1) and the CDMA 2000. When a radio terminal UEperforming communication using the LTE (the frequency band F2) movesinto the coverage hole of the LTE (the frequency band F2), the radioterminal UE is able to continuously perform communication by performinghandover to the LTE base station of the frequency band F1 or the CDMA2000 base station.

A coverage hole of the CDMA 2000 is covered by the LTE (the frequencyband F1) and the LTE (the frequency band F2). When a radio terminal UEperforming communication using the CDMA 2000 moves into the coveragehole of the CDMA 2000, the radio terminal UE is able to continuouslyperform communication by performing handover to the LTE base station ofthe frequency band F1 or the LTE base station of the frequency band F2.

Meanwhile, at a location where the coverage holes of the LTE (thefrequency band F1), the LTE (the frequency band F2), and the CDMA 2000overlap one another, since it is probable that communication of theradio terminal UE in a connected state is interrupted, it is necessaryto quickly perform handling.

Accordingly, it is important for an operator to recognize whether thecoverage hole at one frequency band of one RAT is covered by the otherRAT and/or the other frequency band.

(2) Configuration of LTE Base Station

FIG. 3 is a block diagram illustrating a configuration of the LTE basestation eNB according to the present embodiment.

As illustrated in FIG. 3, the LTE base station eNB includes an antenna101, a radio communication unit 110, a network communication unit 120, astorage unit 130, and a control unit 140.

The antenna 101 is used for transmitting and receiving a radio signal.The radio communication unit 110 is configured by using a radiofrequency (RF) circuit and a base band (BB) circuit, for example, andtransmits and receives a radio signal via the antenna 101. Furthermore,the radio communication unit 110 modulates a transmission signal anddemodulates a reception signal. The network communication unit 120 isconfigured to perform communication with other network devices (such asthe operation and maintenance device OAM and other LTE base stationseNB). The storage unit 130 is configured by using a memory, for example,and stores different types of information used, for example, forcontrolling the LTE base station eNB. The control unit 140 is configuredby using CPU, for example, and controls various functions provided inthe LTE base station eNB.

The control unit 140 includes a measurement control unit 141 and an MDTdata acquisition unit 142.

The measurement control unit 141 generates an MDT Configuration messagefor setting a measurement parameter in a radio terminal UE, and controlsthe radio communication unit 110 such that the MDT Configuration messageis transmitted to the radio terminal UE. The measurement parameterincludes a frequency band to be measured (measurements to be logged), ameasurement trigger (triggering of logging event), a measurementduration (total duration of logging), an absolute time (network absolutetime stamp), and a measurement area (measurement area). However, themeasurement area (measurement area) may not be included in themeasurement parameter.

The MDT data acquisition unit 142 performs a process of acquiring MDTdata from a radio terminal UE transitioned from an idle state (a standbystate) to a connected state (a state during communication).Specifically, after the radio communication unit 110 receives anRRCConnectionSetupComplete message including holding information (alsocalled as Availability Indicator) indicating that the radio terminal UEholds the MDT data, when it is determined to acquire the MDT data fromthe radio terminal UE by the network, the MDT data acquisition unit 142generates a UEInformationRequest message and controls the radiocommunication unit 110 such that the generated UEInformationRequestmessage is transmitted to the radio terminal UE.

When the radio communication unit 110 receives a UEInformationResponsemessage transmitted (reported) from the radio terminal UE in response tothe UEInformationRequest message, the MDT data acquisition unit 142acquires the MDT data included in the received UEInformationResponsemessage.

Then, the MDT data acquisition unit 142 controls the networkcommunication unit 120 such that the acquired MDT data is transmitted tothe operation and maintenance device OAM. In addition, as well as thecase in which the MDT data is transmitted to the operation andmaintenance device OAM, the MDT data acquisition unit 142 may interpretthe content of the MDT data and use the MDT data in order to optimize aparameter of the LTE base station eNB.

(3) Configuration of Radio Terminal

FIG. 4 is a block diagram illustrating a configuration of the radioterminal UE according to the present embodiment.

As illustrated in FIG. 4, the radio terminal UE includes an antenna 201,a radio communication unit 210, a user interface unit 220, a GPSreceiver 230, a battery 240, a storage unit 250, and a control unit 260.However, the radio terminal UE need not include the GPS receiver 230.

The antenna 201 is used for transmitting and receiving radio signals.The radio communication unit 210 is configured by using a radiofrequency (RF) circuit and a base band (BB) circuit, for example, andtransmits and receives a radio signal via the antenna 201. Furthermore,the radio communication unit 210 modulates the transmission signal anddemodulates the reception signal. In the present embodiment, the radiocommunication unit 210 is compatible with each of the LTE (the frequencyband F1), the LTE (the frequency band F2), and the CDMA 2000 (thefrequency band F3). The user interface unit 220 is a display, a button,or the like that functions as an interface with the user. The battery240 is configured to charge an electric power supplied to each block ofthe radio terminal UE. The storage unit 250 is configured by using amemory, for example, and stores different types of information used forcontrolling the radio terminal UE, for example. The control unit 260 isconfigured, for example, using CPU, and controls various functionsprovided in the radio terminal UE.

The control unit 260 includes a first measurement unit 261, a secondmeasurement unit 262, a logging unit 263, and a report processing unit264.

In the connected state, when the radio communication unit 210 receivesthe MDT Configuration message from the LTE base station eNB, the firstmeasurement unit 261 sets the measurement parameter included in thereceived MDT Configuration message.

In the present embodiment, the radio communication unit 210 correspondsto a reception unit that receives the MDT Configuration message forsetting a measurement parameter including a frequency band to bemeasured. As described above, the measurement parameter includes thefrequency band to be measured, the measurement trigger, the measurementduration, the absolute time, and the measurement area. However, themeasurement area may not be included in the measurement parameter.

In the idle state, the first measurement unit 261 performs radioenvironment measurement with respect to an LTE frequency band to bemeasured according to a measurement parameter stored in the storage unit250. In addition, the radio environment, for example, includes referencesignal received power (RSRP) or reference signal received quality(RSRQ).

The second measurement unit 262 performs radio environment measurementwith respect to RAT different from LTE (CDMA 2000 in the presentembodiment) and/or an LTE frequency band other than the frequency bandto be measured. Furthermore, when performing the radio environmentmeasurement with respect to the RAT different from LIE, the secondmeasurement unit 262 may perform the measurement with respect to afrequency band equal to the LTE frequency band to be measured or mayperform the measurement with respect to a frequency band different fromthe LTE frequency band to be measured.

The logging unit 263 logs MDT data including a measurement result of thefirst measurement unit 261, location information, and a time stamp (thatis, stores the MDT data in the storage unit 250). The locationinformation includes ECGI (E-UTRAN Cell Global Identifier) of a servingcell. Furthermore, when the radio terminal UE has a positioningfunction, the location information further includes GNSS (GlobalNavigation Satellite System) location information. Meanwhile, when theradio terminal UE has no positioning function, the location informationfurther includes an RF (Radio frequency) fingerprint related to areception state from a neighboring cell. The time stamp indicates timeinformation employing an absolute time included in the measurementparameter as a reference.

When the measurement result (the RSRP and/or the RSRQ) by the firstmeasurement unit 261 is smaller than a threshold value, the logging unit263 logs MDT data including the measurement result of the secondmeasurement unit 262, location information, a time stamp, and frequencyband information indicating a frequency band at which the measurement isperformed by the second measurement unit 262, in addition to themeasurement result by the first measurement unit 261.

For example, in the case in which a frequency band to be measured is thefrequency band F1, when the second measurement unit 262 performsmeasurement with respect to the LTE frequency band F2, the logging unit263 logs frequency band information indicating the frequency band F2with associating the frequency band information with a measurementresult of the frequency band F2. Furthermore, in the case in which thefrequency band to be measured is the frequency band F1, when the secondmeasurement unit 262 performs measurement with respect to the frequencyband F3 of the CDMA 2000, the logging unit 263 logs frequency bandinformation indicating the frequency band F3 with associating thefrequency band information with a measurement result of the frequencyband F3.

The report processing unit 264 performs a process of reporting held MDTdata to the network. Specifically, when the radio terminal UE istransitioned from the idle state to the connected state, the reportprocessing unit 264 transmits, to the network, holding information(Availability Indicator) indicating that the MDT data is held.Specifically, the radio terminal UE allows the holding information to beincluded in an RRCConnectionSetupComplete message indicating that thesetup of the connected state is completed, and transmits theRRCConnectionSetupComplete message to the network.

Then, when the radio communication unit 210 receives theUEInformationRequest message that requests the transmission of the MDTdata, the report processing unit 264 controls the radio communicationunit 210 such that the UEInformationResponse message including the heldMDT data is transmitted to the network. In the present embodiment, thereport processing unit 264 and the radio communication unit 210correspond to a transmission unit configured to transmit the MDT dataincluding frequency band information to be, which is included in theUEInformationResponse message.

(4) Radio Measurement Collection Method

Next, a radio measurement collection method according to the presentembodiment will be described in the sequence of (4.1) Entire schematicoperation and (4.2) Logging process.

(4.1) Entire Schematic Operation

FIG. 5 is an entire schematic sequence diagram illustrating the radiomeasurement collection method according to the present embodiment.

As illustrated in FIG. 5, in step S11, the LTE base station eNB includedin the E-UTRAN transmits an MDT Configuration message to the radioterminal UE in a connected state. The radio terminal UE receives the MDTConfiguration message.

In step S12, the radio terminal UE sets a measurement parameter includedin the received MDT Configuration message. Furthermore, the radioterminal UE activates a measurement duration timer (duration timer).

In step S13, the radio terminal UE is transitioned from the connectedstate to an idle state.

In step S14, the radio terminal UE performs radio environmentmeasurement according to the measurement parameter, and logs MDT dataincluding a measurement result, location information, and a time stamp.Such a process may be called as “logging”. Details of the loggingprocess will be described later.

In step S15, the radio terminal UE performs a connection process withthe LTE base station eNB included in the E-UTRAN. Furthermore, it ishighly probable that the LTE base station eNB serving as a connectiondestination is different from a transmission source base station of theMDT Configuration message.

In step S16, the radio terminal UE transmits anRRCConnectionSetupComplete message including holding information(Availability Indicator) to the LTE base station eNB. The LTE basestation eNB receives the RRCConnectionSetupComplete message. Inaddition, at the time point at which the LTE base station eNB is able tocorrectly receive the RRCConnectionSetupComplete message, the radioterminal UE completes transition to the connected state from the idlestate.

In step S17, when MDT data is acquired from the radio terminal UE, theLTE base station eNB transmits a UEInformationRequest message to theradio terminal UE. The radio terminal UE receives theUEInformationRequest message.

In step S18, the radio terminal UE transmits a UEInformationResponsemessage including the MDT data to the LTE base station eNB in responseto the UEInformationRequest message. When the UEInformationResponsemessage is received, the LTE base station eNB transmits the acquired MDTdata to the operation and maintenance device OAM. In addition, the LTEbase station eNB may interpret the content of the MDT data and may usethe MDT data in order to optimize its own parameter.

(4.2) Logging Process

Next, the logging process (that is, details of step S14 of FIG. 5) willbe described. FIG. 6 is a flowchart illustrating details of the loggingprocess.

In step S141, the first measurement unit 261 of the radio terminal UEconfirms whether an event corresponding to a measurement triggerincluded in the measurement parameter that is set from the LTE basestation eNB occurs. When the event occurred, the procedure proceeds tostep S142.

In step S142, the first measurement unit 261 performs measurement of aradio environment (specifically, RSRP and RSRQ) with respect to afrequency band to be measured included in the measurement parameter thatis set from the LTE base station eNB. Furthermore, the first measurementunit 261 performs measurement with respect to LTE.

In step S143, the second measurement unit 262 performs measurement of aradio environment (specifically, RSRP and RSRQ) with respect to RATdifferent from LTE (CDMA 2000 in the present embodiment) and/or an LTEfrequency band other than the frequency band to be measured.

In step S144, the logging unit 263 compares the RSRP measured by thefirst measurement unit 261 with a threshold value 1 and compares theRSRQ measured by the first measurement unit 261 with a threshold value2. When the RSRP and the RSRQ are equal to or more than the thresholdvalues, the procedure proceeds to step S145. Meanwhile, when at leastone of the RSRP and the RSRQ is smaller more than the threshold values,the procedure proceeds to step S146.

In step S145, the logging unit 263 logs MDT data corresponding to stepS142, that is, MDT data including the measurement result (the RSRP andthe RSRQ) in step S142, location information indicating a location whenthe measurement was performed in step S142, and a time stamp indicatinga time when the measurement was performed in step S142.

Meanwhile, in step S146, the logging unit 263 logs the MDT datacorresponding to step S142 and MDT data corresponding to step S143.Specifically, in addition to the MDT data including the measurementresult (the RSRP and the RSRQ) in step S142, the location informationindicating the location when the measurement was performed in step S142,and the time stamp indicating the time when the measurement wasperformed in step S142, the logging unit 263 logs MDT data including themeasurement result (the RSRP and the RSRQ) in step S143, locationinformation indicating a location when the measurement was performed instep S143, a time stamp indicating a time when the measurement wasperformed in step S143, and frequency band information indicating afrequency band at which the measurement was performed in step S143. Inaddition, the logging unit 263 may use the location information and thetime stamp that are common in the MDT data corresponding to step S142and the MDT data corresponding to step S143.

In step S147, the first measurement unit 261 confirms whether expirationof a measurement duration or transition to a connected state occurs.When there is the occurrence of the expiration of the measurementduration or the transition to the connected state, the logging processis ended. Meanwhile, when there is no occurrence of the completion ofthe measurement duration or the transition to the connected state, theprocedure returns to step S141.

In addition, in step S145, the logging unit 263 logs only the MDT datacorresponding to step S142. However, the logging unit 263 may log theMDT data corresponding to step S143.

(5) Effect of Embodiment

As described above, according to the present embodiment, when the RSRPor the RSRQ from the LTE base station eNB is smaller than a thresholdvalue (that is, a coverage hole), the radio terminal UE, which receivedthe measurement parameter set from the LTE base station eNB, logs ameasurement result for RAT different from LTE and/or an LTE frequencyband other than the frequency band to be measured, the locationinformation, and the time stamp. In this way, it is possible torecognize whether a coverage hole at one frequency band of LTE iscovered by another RAT and/or another frequency band.

Furthermore, in the present embodiment, the radio terminal UE logsfrequency band information when radio environment measurement wasperformed with respect to the RAT different from LTE and/or the LTEfrequency band other than the frequency band to be measured, togetherwith the measurement result, the location information and the timestamp. Moreover, in the present embodiment, the radio terminal UEtransmits, to the network, the UEInformationResponse message includingthe logged measurement result, location information, time stamp, andfrequency band information. In this way, it is possible to recognize RATand/or a frequency band that covers the coverage hole at one frequencyband of LTE.

(6) Other Embodiments

While the present invention has been described by way of the foregoingembodiments, as described above, it should not be understood that thestatements and drawings forming a part of this disclosure limit theinvention. Further, various substitutions, examples, or operationaltechniques shall be apparent to a person skilled in the art on the basisof this disclosure.

For example, in the aforementioned embodiment, the mobile communicationsystem configured on the basis of LTE-Advanced with specificationsdesigned by 3GPP was mainly described. However, the present inventioncan also be applied to a mobile communication system and the likeconfigured on the basis of W-CDMA (Wideband Code Division MultipleAccess), as well as the LTE-Advanced. For example, a measurementparameter may be set from a W-CDMA (UMTS) base station to a radioterminal.

Thus, it must be understood that the present invention includes variousembodiments that are not described herein.

In addition, the entire content of Japanese Patent Application No.2010-227815 (filed on Oct. 7, 2010) is incorporated in the presentspecification by reference.

INDUSTRIAL APPLICABILITY

As described above, according to the radio measurement collection methodand the radio terminal of the present invention, it is possible torecognize whether a coverage hole at one frequency band of one RAT iscovered by another RAT and/or another frequency band, so that the radiomeasurement collection method and the radio terminal are available forradio communication such as mobile communication.

The invention claimed is:
 1. A radio measurement collection methodperformed by a radio terminal, comprising the steps of: receiving, froma radio base station of a first radio access technology, a Minimizationof Drive Test (MDT) configuration specific to the first radio accesstechnology; in an idle state, performing radio environment measurementin accordance with the MDT configuration, wherein the radio terminalperforms second measurement for a second radio access technology as wellas first measurement for the first radio access technology even when theMDT configuration only configures the first measurement for the firstradio access technology; in the idle state, logging measurement resultsof the radio environment measurement together with location information,wherein the radio terminal logs a second measurement result for thesecond radio access technology as well as a first measurement result forthe first radio access technology so as to perform a report to anetwork; and transmitting the first measurement result and the secondmeasurement result to the network, the second measurement resultincluding information of frequency at which the second measurement isperformed.
 2. The radio measurement collection method according to claim1, further comprising a step of transmitting, from the radio terminal toa radio base station of the first radio access technology, notificationinformation indicating that the radio terminal has the measurementresults, when the radio terminal is transitioned from the idle state toa connected state.
 3. A radio terminal comprising: a receiver thatreceives, from a radio base station of a first radio access technology,a Minimization of Drive Test (MDT) configuration specific to the firstradio access technology; a controller that, in an idle state, performsradio environment measurement in accordance with the MDT configuration,wherein the controller performs second measurement for a second radioaccess technology as well as first measurement for the first radioaccess technology, even when the MDT configuration only configures themeasurement for the first radio access technology; and logs measurementresults of the controller together with location information, whereinthe controller logs a second measurement result for the second radioaccess technology as well as a first measurement result for the firstradio access technology so as to perform a report to a network; and atransmitter that transmits the first measurement result and the secondmeasurement result to the network, the second measurement resultincluding information of frequency at which the second measurement isperformed.
 4. A processor for controlling a radio terminal, configuredto: receive, from a radio base station of a first radio accesstechnology, a Minimization of Drive Test (MDT) configuration specific tothe first radio access technology; in an idle state, perform radioenvironment measurement in accordance with the MDT configuration,wherein the processor performs second measurement for a second radioaccess technology as well as first measurement for the first radioaccess technology, even when the MDT configuration only configures themeasurement for the first radio access technology; in the idle state,log measurement results of the radio environment measurement togetherwith location information, wherein the processor logs a secondmeasurement result for the second radio access technology as well as afirst measurement result for the first radio access technology so as toperform a report to a network; and transmit the first measurement resultand the second measurement result to the network, the second measurementresult including information of frequency at which the secondmeasurement is performed.